Anyway here are some of the everyday visitors to the garden taken with the Sigma set at about 450mm most of the time:
Adult Goldfinch
Young Goldfinch
Young Sparrows at the bird bath
Sparrow enjoying Elder berries
Robin
Greenfinch trying to keep its balance
Greenfinch
The lighting conditions were not very kind as the Sun was often hidden behind cloud. I had upped the ISO to cope but even so I still found the results disappointing as the Sigma had had good reviews. Mine is second hand so maybe it is not in perfect condition optically. Also there is the difference in price to take in to consideration as the Canon lens cost an arm and a leg whereas the Sigma only needs an arm!